fix panel resizing issues

[zisoft]

This PR fixes some issues with the panel resizing reported by @rexbron in #20175.
I don't know if this is macOS specific, or occurs on all platforms.

When the right panel border is dragged to the left to increase its width, the middle panel (thumbtable) is shrinked to make room. When the middle panel reaches its minimum allowed size and the panel border is dragged further to the left, the darktable application window is grown to the right:

resize1.mp4

Now switch to fullscreen mode and repeat the steps. The right panel width gets stuck and cannot be resized again:

resize2.mp4

fixes #20175
fixes #19223

[hfiguiere]

While this patch indeed prevent the behaviour from #19223, aka the window resizing in lieu of the side bar, it prevent making the sidebar a usefull size.

This is the widest it allow me:

[hfiguiere]

Note that before the issue occured, I could resize the side bar to a usefull size.

Reducing the number of thumbnail per row from 4 to 3 just make them bigger. No change otherwise.

[zisoft]

@hfiguiere : thanks for the feedback.

Strange, I cannot reproduce.
Can you please check your darktablerc for max_panel_width=1500

[hfiguiere]

Yes it has this.
max_panel_width=1500

I never set it.

[zisoft]

Does it work with a fresh config?

[zisoft]

This is how it works on my side:

dt.mp4

[hfiguiere]

I deleted the line max_panel_width=1500

Then I can have this width in the "culling" layout. But if I switch back to "filemanager", the problem described in #19223 occur, until I resize the panel, but then the comment #20610 (comment) applies. See the screencast below.

Screencast.From.2026-03-21.11-46-57.webm

[hfiguiere]

And max_panel_width=1500 is back after that.

[hfiguiere]

It seems the that problem only occur in the "filemanager" view.

[zisoft]

Works for me in all layout types...
Can you please try with a fresh config?

[TurboGit]

I'll need to have a deeper review as this seems a patch larger than what I would have expected.

[hfiguiere]

I moved (saved) both darktablerc and darktablerc-common and then tried again. It seem to work. Now I need to figure out what parameter is the one causing the problem.

[hfiguiere]

Then I can have this width in the "culling" layout. But if I switch back to "filemanager", the problem described in #19223 occur, until I resize the panel, but then the comment #20610 (comment) applies. See the screencast below.

I think I found the cause.

It's the top bar that prevent widening the side panel further (the one with the filtering) and it doesn't shrink further. Hiding the top bar allow allow widening the right panel further.

And on the screencast above the reason it work with the "cull" layout is because the left panel was hidden. So it had more room.

However there are still some of the original issues.

Hide the left panel. With the top bar visible, widen the right panel as much as possible. Then show the left panel. Things are pushed out to the right. See:

Screencast.From.2026-03-21.21-26-08.webm

Edit: The top bar has less filters than in the previous screencast, so it can shrink more.

[zisoft]

@hfiguiere : Many thanks for the report, I will look into this.

[zisoft]

@hfiguiere , @TurboGit :

I have now tested all use cases, can you please check again?

[hfiguiere]

Still pushes out. On overall the situation is better than before.

Screencast.From.2026-03-22.14-45-21.webm

[zisoft]

In darktablerc we have a new value: min_center_width=650

Can you please test if increasing this value makes any difference on your system?

[hfiguiere]

I set it to 850 and it seems to not push out.

[zisoft]

Ok, I can reproduce if I increase the DPI setting in the preferences.

[zisoft]

@hfiguiere : Can you please set back min_center_width=650 and test again with my latest commit.

TIA